The present disclosure relates generally to the field of ophthalmics, more particularly to ophthalmic devices, including intraocular lenses (IOLs) such as accommodating intraocular lenses.
A healthy young human eye can focus an object in far or near distance, as required. The capability of the eye to change back and forth from near vision to far vision is called accommodation. Accommodation occurs when the ciliary muscle contracts to thereby release the resting zonular tension on the equatorial region of the capsular bag. The release of zonular tension allows the inherent elasticity of the lens to alter to a more globular or spherical shape, with increased surface curvatures of both the anterior and posterior lenticular surfaces.
The human lens can be afflicted with one or more disorders that degrade its functioning in the vision system. A common lens disorder is a cataract which is the opacification of the normally clear, natural crystalline lens matrix. The opacification can result from the aging process but can also be caused by heredity or diabetes. In a cataract procedure, the patient's opaque crystalline lens is replaced with a clear lens implant or IOL.
In conventional extracapsular cataract surgery, the crystalline lens matrix is removed leaving intact the thin walls of the anterior and posterior capsules together with zonular ligament connections to the ciliary body and ciliary muscles. The crystalline lens core is removed by phacoemulsification through a curvilinear capsularhexis i.e., the removal of an anterior portion of the capsular sac.
After a healing period of a few days to weeks, the capsular sac effectively shrink-wraps around the IOL due to the capsularhexis, the collapse of the walls of the sac and subsequent fibrosis. Cataract surgery as practiced today causes the irretrievable loss of most of the eye's natural structures that provide accommodation. The crystalline lens matrix is completely lost and the integrity of the capsular sac is reduced by the capsularhexis. The “shrink-wrap” of the capsular sac around the IOL can damage the zonule complex, and thereafter the ciliary muscles may atrophy. Thus, conventional IOL's, even those that profess to be accommodative, may be unable to provide sufficient axial lens spatial displacement along the optical axis or lens shape change to provide an adequate amount of accommodation for near vision.
It is known to implant a combination of lenses to address refraction errors in the existing lens in the case of phakic IOLs or improve the refractive results of standard IOL after cataract surgery in the case of pseudophakic patients. These “piggyback” IOLs can be placed anterior to the previously implanted IOL or natural lens to improve the refractive results of cataract surgery in the case of pseudophakes or to change the refractive status of the eye in the case of phakic eyes, usually to correct high myopia. Generally, these lenses are implanted in the sulcus and are non-accommodating.